Devices configured to hold certain objects in a container that stores a liquid are required in some cases. For example, when the objects are cell aggregates, for the purpose of sorting, observation, cultivation, and the like of the cell aggregates, a plate including a large number of cell holding portions may be arranged in a cell culture liquid stored in the container, thereby holding the cell aggregates in the holding portions. Japanese Translation of PCT International Application publication No. 2009-504161 discloses a holding device configured to hold cells or beads for biological tests on a plate having a plurality of through holes formed as the cell aggregate holding portions.
In the holding device, it is generally desired that one cell aggregate be held in one holding portion. However, it is difficult to achieve such a desired holding state for cell aggregates. Specifically, when cell aggregates are to be held in the holding portions, a cell suspension containing a large number of cell aggregates is discharged from a dispenser tip into the cell culture liquid in the container. Positioning of the cell aggregates in the holding portions on the plate depends solely on natural precipitation that occurs after the discharge. Therefore, in many cases, the cell aggregates are carried on the plate in a state in which a plurality of cell aggregates are concentrated, or a large number of holding portions remain with no cell aggregates held therein.
As a measure to solve this problem, the plate is vibrated after the cell suspension is discharged. The vibration of the plate may raise such an expectation that the precipitated cell aggregates are dispersed. However, the holding device including a vibration device has a complicated structure. Further, when the holding portion has a shape of a recess and once the cell aggregates are caught in the recess, the cell aggregates cannot be released from the recess with a slight vibration. As a result, the effect of dispersing the cell aggregates may fail to meet the expected level.